1) Field of the Invention
This invention relates generally to fabrication of a semiconductor device and more particularly to a method for cleaning complex semiconductor geometries (e.g. high aspect ratio openings) using hydrocarbon and solvents in a repetitive vapor phase/liquid phase sequence.
2) Description of the Prior Art
In semiconductor manufacturing, it is very important to remove contaminants which accumulate on semiconductors during fabrication. Contaminants can cause high resistance, adhesion problems for subsequent layers, reduced insulation, and other performance and reliability problems. Typically, liquid cleaning processes are used to remove contaminants. However, as device geometries continue to shrink, it becomes difficult for liquid cleaning agents to adequately penetrate vias and other complex geometries. Also, as geometries continue to shrink, performance margins decrease and the cleanliness level of semiconductors must increase. Liquid cleaning agents can recontaminate a semiconductor with contaminants previously removed and suspended or dissolved in the cleaning agent.
The importance of overcoming the various deficiencies noted above is evidenced by the extensive technological development directed to the subject, as documented by the relevant patent and technical literature. The closest and apparently more relevant technical developments in the patent literature can be gleaned by considering the following patents.
U.S. Pat. No. 5,494,526 (Paranjpe) shows a method for cleaning semiconductor wafers using liquified gases. Paranjpe teaches introducing a liquid phase cleaning agent to the surface of a semiconductor wafer, then causing the liquid phase cleaning agent to change to a vapor phase using vibration, heat, pressure, or a combination thereof. Paranje also teaches that the cleaning agent can penetrate into the intricate topography of the semiconductor substrate surface in vapor phase, then condense to remove particulates and contaminants in difficult to reach (e.g. small) openings. The cleaning agent can be: liquefied argon, liquefied nitrogen, non-polar (e.g. N2, O2, CO2) or alkaline (NH3) liquified gases, Freon, or acidic liquified gases (e.g. HCl, HBr, HF, SO3). The cleaning agent is removed by flash evaporation using a rapid pressure drop (e.g. vacuum). If multiple cleaning steps are required to adequately clean the wafer, the entire sequence is repeated.
U.S. Pat. No. 5,990,014 (Wilson) shows a wafer cleaning process using hydrocarbons and vaporous acids.
U.S. Pat. No. 5,055,138 (Slinn) teaches a vapor cleaning process using a highly fluorinated organic cleaning agent and a flammable solvent, with a recycling condensation process. This invention does not address removing the cleaning agent from small openings.
U.S. Pat. No. 4,581,101 (Senoune et al.) discloses a method for dry-etching and cleaning using a fluorinated ether gas.
U.S. Pat. No. 5,641,541 (Chen) discloses a method for applying a primer to a wafer surface, in a gaseous state, prior to photoresist application.
U.S. Pat. No. 4,983,548 (Uno et al.) teaches a method of removing electrical charge from a semiconductor device using a volatile organic solvent, then removing the volatile organic solvent by evaporation.
U.S. Pat. No. 5,246,501 (Rodgers et al.) teaches a method of flash drying parts following vapor degreasing.
It is an object of the present invention to provide a method for cleaning semiconductor structures with complex topographies, including very small openings, using hydrocarbon and solvents.
It is another object of the present invention to provide a method for cleaning vias for sub-quartermicron dual damascene devices using hydrocarbon and solvents.
It is another object of the present invention to provide a method according to the previous objects using repetitive vapor phase condensation and revaporization.
It is yet another object of the present invention to provide an economical and effective method for cleaning semiconductor structures with complex topographies.
To accomplish the above objectives, the present invention provides a method for cleaning a semiconductor structure using vapor phase condensation. The semiconductor structure can be cleaned using vapor phase condensation with a thermally vaporized cleaning agent, a hydrocarbon vaporized by pressure variation, or a combination of the two. In the thermally vaporized cleaning agent process, a semiconductor structure is lowered into a vapor blanket in a thermal gradient cleaning chamber at atmospheric pressure formed by heating a liquid cleaning agent below the vapor blanket and cooling the liquid cleaning agent above the vapor blanket causing it to condense and return to the bottom of the thermal gradient cleaning chamber. The semiconductor structure is then raised above the vapor blanket and the cleaning agent condenses on all of the surfaces of the semiconductor structure removing contaminants and is returned to the bottom of the chamber by gravity. In the pressurized hydrocarbon process, a semiconductor structure is placed into a variable pressure cleaning chamber, having a piston which changes the pressure by reducing or increasing the volume of the chamber. The semiconductor structure first exposed to the hydrocarbon in vapor phase, then the piston is lowered to condense the hydrocarbon. A semiconductor structure can be cleaned by either or both of these processes by repetitive vaporization/condensation cycles.
The present invention provides considerable improvement over the prior art. A semiconductor structure having a complex topography can be effectively and economically cleaned using vapor phase condensation. Also, the semiconductor structure is not recontaminated by contaminants which have been previously removed.